ZF 6HP26X - high adaptation values

[wpoll]

So... been looking into my aging ZF 6HP26X and considering my next move..

But first a little history..

Got the car a decade and 120,000kms ago. Full dealer service history and no mention of any transmission work.

When I first got the car, I asked the dealer to check the transmission as it had a bad 2-1 slam - they said they checked the fluid level and condition (fine and fine) and said they reset the transmission adapations.

Didn't help so I learned to drive around the 2-1 slam (easy enough).

Four years and 30,000kms later, I replaced the power divider oil on the transfer case and reset the VTG oil wear adaptations using DIS. No issue but... the 2-1 slam was gone!! What the heck... I'll take the win...

Fast forward another year or so and the 2-1 slam was back (like the cold, it creeps in...). I knew the mechatronic seal on the transmission was starting to weep a little, so I bit the bullet and replaced it, along with the bridge seal and the four "jump" seals, pan gasket and filter. I used the old fluid again, as I was worried about causing an issue with a full fluid change. I did use a liter or two of new fluid, as you always lose some doing a mechatronic drop (most of it was on me!).

In the last six months, the shifting has gotten noticeably harsher. Not bad but I noticed it, as a I drive the car pretty much every day.

OK - time to try a fluid change. Yeah, I know - a fluid change isn't going to fix hard wear on parts but I figured I'd be dropping the pan again and so I wanted to get as much new fluid into it as possible when I DO drop the pan. Rather than doing 2-3 drain/fills after putting new parts in there, I opted to do the first 2 drain/fills, then drop the pan etc.

Car was now 20 years old and at 285,000kms - on factory fluid.

First drain/fill caused no issues - shifts largely unchanged, possibly a bit smother (plecibo?).

Drove it for a month (500kms?) and then did a second drain/fill. Again, no issues. Initially, anyway. Ater about 200kms it suddenly developed a nasty jerk in 5th gear at low rpm (~1,500rpm). And I mean nasty. It's like the power is chopped hard on/off for a quarter second or so. This repeats 2-3 times in a couple of seconds, then it settles down.

Higher rpm (over 2,000rpms) and high loads (pulling a loaded trailer up a hill at 100km/h in 5th gear) are fine. Sweet as. Zero issues - that I can feel anyay!

Same issue in D, S or M mode. Makes no difference.

Around town, it drives fine - but then it never gets higher than forth gear, so the problem doesn't bite.

Hmmmm... So I load up ISTA and query the solenoid adaptation values....



Not good. They are all way high... way, way high....

Fill times seem ok - at least the first three.

So are high adaptation values on all solenoids a sign of overall low fluid pressure? Is my pump failing or the bridge seal leaking badly?

I was thinking I needed to replace the solenoids but given the fact the adaptations are all high, I don't think this is (just) a solenoid issue.

I guess I'm looking at a full mechatronic rebuild but I'm not throwing over $2k at this only to find the issue remains...

I do so hate loving this car...

[andrewwynn]

If it's worn seals you may get a repreive with ATP AT-205.

When i bought my latest x, the opg was already leaking at 144k. I really didn't want to go through the massive job so to punt i added AT-205 And the drips basically stopped. Now I'm at 195k (miles) still just add 205 when the drips come back after an oil change.

[X5only]

The mechatronic can be rebuilt for around $600 if DIY. It's not hard. I've been having that nasty jerk in 2-3 gear which would happen once and then settles down. It would happen when the car is cold. I did change the VTG oil and reset it and the jerks somewhat subsided but was still there. I'm currently preparing to do the mechatronic rebuild. Like you, I opted to do 3 drain/fills (with Valvoline MaxLife) before dropping the pan (the trans has never been serviced since I bought the vehicle CPO in 2008 from the dealership). I found the oil was low and very dirty with a slight burnt smell. I can tell you the oil changes results so far have been impressive - smooth gear changes. Tomorrow I'm doing the 4th drain, and I'll drop the pan then and begin the mechatronic rebuild.

Very helpful videos of valve body rebuild:
www.youtube.com/watch?v=W7DZbrvrI5k&t=1073s
www.youtube.com/watch?v=Ct8qbmDXqjs
www.youtube.com/watch?v=XJAuTRKVn88
www.youtube.com/watch?v=YeLFFkx94Jg

[wpoll]

X5only - I would absolutely have a go at the mechatronic rebuild if it was only $600 but the solenoids alone cost around $1k here. There’s nearly $500 in other parts and fluids etc. Lifeguard 6 is around $80 per litre here.... hence using the Maxlife at $15 per litre.

A shop will charge well north of $2k if I take the mechatronic in...

So like I said, I’d rather try to diagnose the issue before I fire the parts cannon. If the high values indicate a mechatronic issue, in I go but I’ve seen a few folk do this only to have to replace bushes and clutch materials anyway, after the mechatronic work failed to address the issues. I don’t want to be in that club...

I’m going to do some more homework on what the high adaptation values mean. The issue I have affects 5th gear and this gear is engaged when the solenoids related to the B and E clutches are off - providing maximum pressure to these two clutches. So if the jerk I feel is a massive slip, does that mean the maximum pressure is too low? I need to read up more to better understand how the adaptation values work and what issue has pushed these values up so high.

There’s a lot to learn...

[80stech]

If I was better with posting I would place a "Bat Signal" shining to get the attention of RRPhil on this thread!

[RRPhil]

I’m not familiar with ISTA, but is it capable of monitoring and recording live values for solenoid currents, speeds, etc.? If so, what are the chances that you could capture your low engine speed 5th gear event?

On the L322 Range Rovers with the 6HP26X transmission, a piece of diagnostic kit called the GAP IIDTool can be used to record exactly what’s going on and generate .csv files with the captured data so you can produce graphs similar to the ones below showing, for example, the solenoid activity. This can be very helpful for analysing exactly what’s going on. It’s worth bearing in mind though that the transmission doesn’t have any pressure transducers so you’re only measuring solenoid current and having to assume that the pressure is following the same characteristic. Clearly this may not be the case if a solenoid is faulty.

Just a few points from me, in the unlikely event they’re helpful:

As you have already mentioned, in 5th gear all the EDS solenoids are electrically ‘off’ (well, more accurately, they’re at their minimum current of 0.048A). EDS 1 & EDS 3 (yellow cap solenoids) will therefore be producing almost no pressure and EDS 2 & EDS 4 (blue cap solenoids) will be producing maximum pressure (regulated to 5 bar). The B-clutch (controlled by EDS 2) and E-clutch (controlled by EDS 4) are therefore engaged.



The EDS solenoids only modulate the clutch pressures during the actual gearshifts. Once the oncoming gear is engaged the holding valve for that particular clutch latches on and the clutch then operates at mains system pressure, which is dictated by solenoid EDS 5 (blue cap). The EDS solenoid (1, 2, 3 or 4) for that particular gear is then either electrically ‘on’ (0.848A) or ‘off’ (0.048A) and has no influence on the pressure applied to the clutch pack.



EDS 6 (yellow cap solenoid) controls the application of the torque converter lock-up clutch, and it’s also worth monitoring what it is doing as well, because a fault with the LUC can also feel similar to one of the transmission clutches slipping.



Phil

[wpoll]

RRPhil - many thanks for jumping in and adding additional information - all very useful.

I'm not all that familiar with ISTA either - to date I've managed with INPA and DIS (the tools that were current when my car was made) and have only started using ISTA to drill down into this issue.

I'll be spending some more time on ISTA and see if I can generate the data points as you suggest.

I'm going to look very closely at the LUC first I think, since as you mention, the LUC letting go would feel very much like a clutch slip. In fact, the more I think about this problem and the symptoms, the LUC stands out as a strong contender for causing the issue.

On my drive to work today, the transmission performed nearly faultlessly - even in 5th gear. I didn't exactly try to provoke the fault, but I used a small section of higher-speed road where I could travel at 70km/h and the car engaged 5th gear and held it without issue. Very smooth operation in fact.

Time to dig into the ZF manuals a bit more, methinks!

(oh, and RRPhil - did you have any thoughts on the high adaptation values - something to worry about?)

[RRPhil]

Automatic transmission friction elements have 3 phases of engagement. The first, the pre-charge phase, is where the back of the empty clutch piston is filled by the hydraulics, pushing against the piston return spring until the plate clearances are taken up. The clutch isn’t capable of transmitting torque during this phase, it’s just primed and ready. This ‘rapid fill’ or ‘quick charge’ phase can be seen in the measured trace below, where the current for the oncoming solenoid spikes to achieve the rapid fill and then drops back again.
The duration of the spike is the rapid fill time, in this case for a 5-6 upshift with the C-brake engaging, and the clutch fill pressure can also be seen.



Over a period of time (i.e. years) the clutch friction plates will naturally wear slightly and the clutch piston movement required to take up the clutch pack clearance will therefore increase. Hence the need for the adaptions/adaptations to make the necessary minor adjustments to cater for this wear.

The controller also adapts the clutch pressure during the second phase of the shift, where the clutch is transmitting torque to engage the next gear by bringing the slip speed to zero. It does this by measuring the rate of change of the turbine speed during the shift, and if the gradient is too steep it backs off the pressure slightly, or increases it if the rate of speed change is too slow.

A single high adaption value often indicates a fault with a particular solenoid or a leak in a particular clutch’s hydraulic circuit (a worn rear stator bush for the E-clutch, being an obvious example) but, in your case, the fact that the adaption/adaptation values are high for all the clutches may just be an indication that the transmission has done a high mileage and is generally just ‘worn’.

One thing you could try is to remove the Mechatronic unit and carry out an air pressure test on each clutch feed port to check that there’s no excessive leakage in any of the clutches.

Phil

[X5only]

I was curious what the adaptations are for my transmission (mileage 168K miles) since I'm going to overhaul the mechatronic today. Here they're for comparison's sake. Phil, what is the threshold for the values to be indicative of an issue? Are my numbers, ok? Thanks!

[wpoll]

Thanks again, RRPhil - that all makes perfect sense.

It also aligns with some further thoughts I've had (probably as you wrote your response!) - I am now thinking that I'm wrong in thinking the "high" valvue shown in ISTA are a problem - I think they simply show an old, worn transmission.



And here's my thinking...

The ISTA values shown above are on a screen labelled "existing adaptation values" but are then listed as "clutch fill pressures". To me, these clutch fill pressure now appear to be actual stored pressure values (in mbar) and not an offset from some nominal value. If so, they are NOT way high - they are all about what you would expect to see in an older transmission.

ZF state the adaptation limits thus: -



These are negative and positive mbar and ms offsets, applied to some nominal base value. I don't think these correlate directly to the values shown in ISTA as I had initially assumed. For one, ISTA is NEVER going to show a negative pressure value!!

This is clearly shown in this screen grab from one of Mickey Figueroa's great YouTube videos, where the -30mbar offset is shown as being applied to a nominal 600mbar pressure value, giving a stored pressure value of 570mbar.



So what I had assumed were out-of-spec adaptation offset values are in fact likely to be stored pressure values, after the adaptation offset has been applied. I'll dig deep into ISTA and see if I can locate the actual stored offset values but I didn't spot them on the first (or second!) look.

In light of this, I no longer think my adaptations are out-of-spec. Not knowing what the nominal pressure values are for each clutch but assuming that 600mbar might be typical, I think my offsets are still well within the limits stated by ZF. They also align with what both RRPhil and Mickey Figueroa indicate, that worn transmissions usually exhibit positive adaption offset values.

So now to figure out what the issue actually is!

*edit* Hang on!! - I missed that clutch D is showing a value of 200mbar - that's -400mbar below the nominal 600mbar value - so that may be worth looking into!